Could Bug Spray Attract Mosquitoes? Lab Insects Learned That the Smell of DEET Would Lead Them to a Tasty Treat

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A mosquito drinking blood from a bag, accessible through mesh<br>Romina Barrozo

Summer is almost here in the Northern Hemisphere, and that means a seasonal menace is on the horizon: mosquitoes. They aren’t just minor annoyances during outdoor activities—they also carry deadly diseases.

When trying to protect yourself from the pests, you probably douse yourself in bug spray, particularly varieties with the active ingredient DEET. Now, however, researchers have demonstrated that in the lab, mosquitoes can learn to associate off-putting DEET with a blood meal and become attracted to the scent. The findings, described in a study published May 28 in the Journal of Experimental Biology, reinforce that we should regularly reapply insect repellent and highlight what scientists still don’t know about how DEET affects mosquitoes.

“The general consensus was that repellents worked solely because of their chemical properties: Either they were toxic or unpleasant to mosquitoes, driving them away, or they blocked their ability to detect humans,” study co-author Claudio Lazzari, a behavioral physiologist at the University of Tours in France, tells the Australian Broadcasting Corporation’s Ellen Phiddian.

Although scientists still aren’t sure why mosquitoes dislike bug spray, the new study, along with other recent research, indicates that the insects’ reactions to it are more malleable than once thought, he adds, although this is the first work to find that DEET can draw them in.

Lazzari and his colleagues worked with a lab-bred variety of Aedes aegypti mosquitoes. In the wild, this species can carry dangerous viruses, including those that cause yellow fever, dengue, chikungunya and Zika.

The researchers trained the pests to associate DEET with food by introducing a bag of warm sheep’s blood into the mosquitoes’ enclosures for 30 seconds. During the last ten seconds of mealtime, they wafted in the unpleasant compound. They completed the process four times.

When DEET filled the insects’ space again, more than 60 percent of them tried to slurp blood from an out-of-reach blood bag.

Did you know? Humans have had a long relationship with mosquitoes

Mosquitoes have been biting people for more than one million years, researchers reported earlier this year. They evolved a taste for human blood around the time when Homo erectus migrated into Southeast Asia. Most of the 3,500 mosquito species that exist today don&rsquo;t drink our blood, though.

Then, researchers ramped up the tests with a live snack source: study co-author Ayelén Nally, a chemical ecologist at the University of Buenos Aires in Argentina. When she offered both her hands—one doused in DEET—to the trained mosquitoes, about 60 percent of them attempted to go after the repellent-covered one, per a statement. The mosquitoes also learned to associate DEET with a sugary treat.

“The new study shows it’s possible to condition mosquitoes to bite more if they’re repeatedly exposed to DEET during a blood meal. Not only does this tell us more about how it repels mosquitoes, but it raises the prospect mosquitoes may actually be attracted towards DEET in some cases,” writes Leon Hugo, a medical entomologist at the University of Queensland in Australia who did not participate in the study, for the Conversation.

People should still wear DEET to protect themselves from mosquitoes, experts say, which carry pathogens that kill more than one million people worldwide each year. The findings suggest that we need to use bug sprays with adequate concentrations of DEET and reapply regularly.

“The study authors state it was challenging to make mosquitoes feed a first time in the presence of DEET, and that the highest risk an association would form is when [the] repellent starts to wear off,” Nina Stanczyk, a chemical ecologist at ETH Zurich in Switzerland who did not participate in the study, tells the Guardian’s Nicola Davis. “Therefore, the most important point for travelers is to regularly reapply repellent as instructed by the product label.”

Study co-author Clément Vinauger, a mosquito researcher at Virginia Tech, agrees. DEET is “still the gold standard in terms of protection,” he tells Science News’ Erin Garcia de Jesús.

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